There's a guy giving away free PCBs for a 3 Ampere (or less), 48 Volt (or less), SMPS filter. It's aimed at analog line level equipment, and the title of the thread says it's intended application is "Preamps, HeadPhone Amps, Korg NuTube, etc."
His generosity is not completely unlimited, of course; have a look at post #399 (here)
His generosity is not completely unlimited, of course; have a look at post #399 (here)
Yes, SMPS supplies do fail and there were many crummy ones made. While you are at the dump, take a look at how many conventional supplies there are there inside most every appliance made over decades. Not limited to SMPS supplies.
If so why any linear / regulated power supply design do not use common mode filters, ferrite beads and so on.
Current linear power supply design focus on lowering the ripple and then use state of art regulators which is so weak / none attenuation performance at high frequencies.
For the linear power supplies there are lots of high frequency content comes from mains and injected in to secondary of the transformer.
If we look at the very top performer dac designs, they do not use any mains emi filter. But still have great objective measurements.
Compared to a switching MOSFET drain jumping up and down between 0 and 300 V at a 100 kHz or so rate, I think the amount of high-frequency rubbish coming from the mains is not that high.
In any case, in the mixed-signal circuits I worked on, there were usually ferrite beads on the boards to separate the digital from the analogue and the supplies from the analogue. Usually these are SMD ferrite beads like the Murata BLM18 series placed right next to sensitive and noisy supply pins.
In any case, in the mixed-signal circuits I worked on, there were usually ferrite beads on the boards to separate the digital from the analogue and the supplies from the analogue. Usually these are SMD ferrite beads like the Murata BLM18 series placed right next to sensitive and noisy supply pins.
Marcel: How would you filter SMPS noise that sounds like a blend of 120Hz and "clock"? 12V 20A max output. By clock I mean it's not a constant HF hash, but you here the feedback "clocking" like when you hear your computer processing through a cheap sound card.
What does it supply? Is that sound the low-frequency content of the SMPS output voltage or is it some frequency conversion product generated in the circuit supplied by it?
It supplies tube heaters, DC-DC boost for B+, and I only hear noise on a high gain low PSRR stage (line stage is quiet even on headphones, but ad 40db and voila). It sounds like 120Hz hum plus HF clock style hash? I haven't tried to filter it at all save for normal RC filtering at the gain stages.
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I guess I would first want to figure out whether there is audible-frequency-range interference present at the SMPS output, or if it is some interaction with the boost converter or a high-frequency ripple with varying amplitude that becomes audible due to parasitic AM demodulation.
You could AC couple the supplies into the input of an amplifier, using diodes to prevent blowing up the amplifier at power-on or -off and using an RC low-pass at 20 kHz. If you hear your hum blend at the 12 V under those conditions, it is apparently due to poor regulation of the switching regulator. A series regulator between the SMPS and anything sensitive should then help. If not, then a filter like dotneck335 referred to might help, although you have to redimension it if it has to handle 20 A.
The fact that you only hear it on a low PSRR stage suggests it goes via the boost converter and B+. If that's correct, you could leave the heater supply untouched.
You could AC couple the supplies into the input of an amplifier, using diodes to prevent blowing up the amplifier at power-on or -off and using an RC low-pass at 20 kHz. If you hear your hum blend at the 12 V under those conditions, it is apparently due to poor regulation of the switching regulator. A series regulator between the SMPS and anything sensitive should then help. If not, then a filter like dotneck335 referred to might help, although you have to redimension it if it has to handle 20 A.
The fact that you only hear it on a low PSRR stage suggests it goes via the boost converter and B+. If that's correct, you could leave the heater supply untouched.
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Then I must have seen a Fata Morgana 🙂 Many new designs use RF protection and many recent regulators are meant for use in RF environments (i.e. cell phone, network devices).
Personally I use beads and common mode filters in linear designs for a very long time. Many quality brands do the same although it may not look like that at first (built in EMI filters). The use of EMI filters at the mains side is meanwhile a necessity when one lives in a city with industry, uses a cell phone, has wireless internet, bluetooth, LED lighting, SMPS adapters for many devices in a home etc.
Choice of mains transformer makes a difference as well.
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According to very detailed test reports here below;
PS Audio Noise Harvester AC Cleaner Review | Audio Science Review (ASR) Forum
and
Review and Measurements of Schiit Yggdrasil V2 DAC | Page 15 | Audio Science Review (ASR) Forum
They simply shows that emi/diff/cm noises which are mainly above 10Mhz do not have any negative effect on such sensitive device like DAC.
PS Audio Noise Harvester AC Cleaner Review | Audio Science Review (ASR) Forum
and
Review and Measurements of Schiit Yggdrasil V2 DAC | Page 15 | Audio Science Review (ASR) Forum
They simply shows that emi/diff/cm noises which are mainly above 10Mhz do not have any negative effect on such sensitive device like DAC.
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I don't think we agree what a mains filter is. I took the time to read the first link and that is no mains filter, that is an plug in audio gadget for people with too much money. It does not seem to do something really useful except blinking a LED which is absolutely not exemplary for real EMI mains filters (these have no LED). So this example proves nothing. Please read something about EMI mains filters and what they do. These are used in industrial (and audio) applications a lot with a reason. The second link has a lot of debating/discourse but apart from 2 measured DACs of which one clearly has PSU issues I can't conclude your remark " It simply shows that emi/diff/cm noises which are mainly above 10Mhz do not have any negative effect on such sensitive device like DAC."
Measurements are nice but beware to have opinions based on just a few tests of a few devices certainly when audio gadgets and a flawed device are used. In both links there is no measurement of an EMI Mains filter.
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Not that big. If it was a power transformer, it'd be under 10VA. Never used them for more than about 50mA.
4.5H
Length: 1.37"
Width: 1.41"
Height: 1.67"
It's coil-58 here: Chokes & Coils
4.5H
Length: 1.37"
Width: 1.41"
Height: 1.67"
It's coil-58 here: Chokes & Coils
I put the choke on the B+ of the boosted 280V supply, not the 12V. It was a wash anyway, what works on the bench doesn't work on the rack. Same clock noise nonsense. Now I'll swap in a passive supply to see if it's RF or something. I can't receive AM radio in this place.